Involvement of alanine racemase in germination of Bacillus cereus spores lacking an intact exosporium

The l-alanine mediated germination of foodisolated Bacillus cereus DSA 1 spores, which lacked anintact exosporium, increased in the presence of d-cycloserine(DCS), which is an alanine racemase (Alr) inhibitor,reflecting the activity of the Alr enzyme, capable of convertingl-alanine to the germination inhibitor d-alanine.Proteomic analysis of the alkaline extracts of the sporeproteins, which include exosporium and coat proteins, confirmedthat Alr was present in the B. cereus DSA 1 sporesand matched to that encoded by B. cereus ATCC 14579,whose spore germination was strongly affected by theblock of conversion of l- to d-alanine. Unlike ATCC 14579spores, l-alanine germination of B. cereus DSA 1 sporeswas not affected by the preincubation with DCS, suggestinga lack of restriction in the reactant accessibility.